Many people can name the eight planets of our solar system but few are familiar with their hosts of natural satellites. While our own moon will be forever dear to us, it has conditioned us to think of the planetary moons as relatively inactive balls of rock. In reality, the planetary moons are fascinating worlds in their own right. Saturn’s moon Iapetus has an equatorial ridge more than four times taller than Mount Everest. Io, one of Jupiter’s four largest moons, boasts approximately 400 active volcanoes. It’s the most volcanically active body in the solar system.

While these moons are fascinating, my personal favorite is Titan, Saturn’s largest moon. Much of what we know about Titan is thanks to the Cassini probe, which has been orbiting Saturn for more than a decade and made 115 flybys of Titan.

Titan is the second largest moon in the solar system and is larger than the planet Mercury. Its atmosphere is mostly nitrogen along with methane and other organic compounds and is so dense that if you were standing on the surface of Titan, the pressure would make it feel like standing on the bottom of a swimming pool. And, like at the bottom of a swimming pool, breathing is not recommended.

Titan also has an interesting topography. Instead of having silicate based rocks like Earth, much of Titan’s terrain is composed of water-ice (as opposed to other ices including CO2 ice, which makes up much of Mars’ polar caps). Titan also has dunes made of dark hydrocarbon materials.

Titan has a methane cycle, which functions like Earth’s water cycle. Titan’s second largest lake, Ligeia Mare, has a volume three times that of Lake Michigan. On the other side of the north pole from these great lakes are a number of much smaller bodies. When enough methane from these seas evaporates into the atmosphere, it eventually begins to precipitate and rain down. Due to the high atmospheric density and low gravity on Titan, methane would likely form melon-sized drops falling slowly through the orange haze.

In some areas on Titan, it even snows methane. Below the surface of Titan lies a large, perhaps global, saltwater ocean over 100 kilometers deep, with a volume comparable to that of the water from all of Earth’s oceans combined. It is possible that this ocean could sustain basic forms of life. Studying these features not only gives us a better understanding of the planetary moons, but also helps us understand analogous features on Earth.